This invention relates to the fabrication of large area nanoimprint molds with complex patterns with minimal or no use of direct-writing, such as electron beam lithography, ion, laser beam, or mechanical beam lithography.
The key challenges in the fabrication of Surface-Enhanced Raman Scattering
(SERS) nanostructures for research and broad applications are to develop nanofabrication technologies that not only can produce smaller SERS nanostructures, but also can produce these nanostructures reliably, with fast turn-around time and over large areas.
The current fabrication approaches cannot meet current needs. Most previous fabrications of nanoantennas have used electron-beam lithography (EBL). Some work has used nanosphere lithography to achieve bowtie structures. EBL offers the capability to write a computer-designed pattern to a substrate and can make structures in the 5 nm range. However, as the feature size gets below 30 nm, not all EBL tools and processes can be used, and the fabrication reliability and throughput are significantly reduced. Nanoscale EBL patterning is limited to an area much less than 1 mm2 area—an area too small to be used as a nanoimprint lithography (NIL) mold. The Table.3B-1 of Appendix 1 shows the time needed for EBL to write arrays of bowtie nanoantennas (with 80 nm ×80 nm triangle pairs, 20 nm gap, and 200 nm and 1 μm pitch) for a 1″ or 6″ wafer. For high resolution patterns, the EBL resists needed (typically PMMA 996K and ZEP520A) are slow. For 20 pA current (needed for smaller beam diameter) it takes about 3 days for writing even 1 μm pitch nanoantenna arrays on a 1″ wafer. Clearly this method is impractical for large-area SERS applications.
Nanosphere lithography has the capability to pattern large areas efficiently, however the controllability and reliability of the pattern positioning are poor. Furthermore the only a limited range of geometric profiles can be patterned by nanosphere lithography.
We have determined that for research scale areas we can speed up the nanofabrication process by using EBL to make a nanoimprint mold, and then use nanoimprint lithography (NIL) to do fast-turn around duplication, rather than use EBL for every nanoantenna fabrication run. It is to be noted that frequently one needs several or 10's of EBL runs to get a single good mold for the required feature scales. However, for larger area applications, there exists a need for further innovative technologies to pattern large-area nanoimprint molds without using EBL.